There has been proposed a method where a communication relaying device relays communication between a device of a user and a device of a communication destination without a direct communication therebetween when the user communicates with the communication destination, thereby concealing a communication identifier used for the communication by the user from the communication destination.
As a related art document disclosing an example of a communication system which uses such a communication relaying device, there is known, e.g. Non-Patent Document 1.
Non-Patent Document 1 discloses a communication system which uses a NAT (Network Address Translation) function as the communication relaying device.
The NAT is a technology used in communication, to which IP (Internet Protocol) used for the Internet is applied, and translates a communication identifier for identifying a communication destination or a communication source. For example, a process to mutually translate a global IP address which is unique on the Internet and a local IP address which is unique within a division is performed.
A communication relaying device which uses the NAT relays communication when the device of the user communicates with the device of the communication destination in a case where the user has a local IP address, for example, and performs a process to translate the local IP address of the device of the user into a global IP address.
In contrast, when the device of the communication destination communicates to the user, the global IP address is translated into the local address of the user. Thus, when the device of the user communicates with the device of the communication destination, it is possible to communicate without disclosing the local IP address which is an IP address of the device of the user to the communication destination, so that it is possible to make it difficult to acquire information on the user from the local IP address.    [Non-Patent Document 1]P. Srisuresh, “Traditional IP Network Address Translator (Traditional NAT)” RFC3022, January, 2001